Solenoid-driven metering systems are well known in the food service arts, and are used for metered dispensing of liquids such as cream and milk, and granular solids such as sugar, for beverages such as coffee and tea. Such systems are sold under the trademark SureShot Dispensing Systems® by A.C. Dispensing Equipment Inc., having an address at 100 Dispensing Way, Lower Sackville, Nova Scotia, Canada B4C 4H2.
FIGS. 1 to 2B show an exemplary prior art solenoid-driven metering system 10. The metering system 10 comprises a flexible dispensing tube 12, a plastic housing 14 surrounding a portion of the dispensing tube 12, and a solenoid plunger 16. Other components of the solenoid-driven metering system, such as the solenoid itself, related control systems, the support structure and other elements have been omitted for clarity of illustration; these elements and their placement will be apparent to one skilled in the art.
Referring specifically to FIG. 1, an upper end 12A of the dispensing tube 12 communicates with a reservoir of the material to be metered (not shown) and a lower end 12B communicates with an outlet (not shown), which may simply be an open end of the dispensing tube 12. In a typical example, the reservoir is a flexible plastic bag containing milk or cream which is sealed except that it opens into an attached dispensing tube 12 to allow the milk or cream to be dispensed. The dispensing tube 12 is arranged generally vertically, with the upper end 12A above the lower end 12B, so that material will flow downwardly through the tube from the upper end 12A to the lower end 12B under the influence of gravity, unless the dispensing tube 12 is constricted.
The housing 14 comprises two opposed halves 14A, 14B removably hingedly secured to one another in a clamshell arrangement by a hinge 18 and securable around the dispensing tube 12 in a closed configuration. Two opposed channels 20A, 20B defined in the tube-receiving faces of the two opposed halves 14A, 14B cooperate to define a vertical passageway 20 through the housing 14 for the dispensing tube 12. The half 14A of the housing 14 facing the solenoid plunger 16 has a plunger aperture 22 which exposes the dispensing tube 12. The housing 14 is maintained in the closed configuration by a thumbscrew 19 that is rotatably journalled in a bore (not shown) through the half 14B of the housing 14 that does not face the solenoid plunger 16 and is threadedly received in a correspondingly positioned threaded aperture 21 (FIG. 1) in the half 14A facing the solenoid plunger 16. The threaded aperture 21 is formed in a metal insert 23 which is in turn secured in a larger aperture in the half 14A facing the solenoid plunger 16, so as to provide improved strength relative to the plastic from which the housing 14 is formed.
Typically, a temperature sensor insert 17 formed from aluminum is installed in the channel 20A in the half 14A facing the solenoid plunger 16. The insert 17 carries a temperature sensor such as a thermistor (not shown) and engages the dispensing tube 12 so that the insert 17 will assume the approximate temperature of the material in the dispensing tube 12 and allow this temperature to be detected by the temperature sensor.
The solenoid plunger 16 comprises a solenoid-actuable armature shaft 24 and a plunger head 26 secured to one end of the armature shaft 24. The plunger head 26 is formed from plastic and comprises a base 28 secured to the armature shaft 24, four support members 30, a disc-shaped portion 32 and a closure member 34. The support members 30 are ogee-shaped and arranged in cruciform relation to one another, and extend outwardly from the base 28 to support the disc-shaped portion 30, which in turn supports the closure member 34.
When assembled, the plunger aperture 22 in the half 14A of the housing 14 facing the solenoid plunger 16 is in registration with the closure member 34 on the plunger head 26.
In operation, as shown in FIGS. 2A and 2B, the solenoid plunger 16 is arranged for reciprocal motion toward and away from the housing 14 under the control of the solenoid (not shown).
The “resting” or “closed” position of the solenoid plunger 16 is shown in FIG. 2A; in this position the closure member 34 on the plunger head 26 has been received in the plunger aperture 22 in the half 14A of the housing 14 facing the solenoid plunger 16, and the plunger 16 may be maintained in this position by, for example, a suitable biasing member such as a spring (not shown). In this position, the closure member 34 compresses the dispensing tube 12 and pinches it against the back wall 36 of the passageway 20 defined by the channels 20A, 20B (FIG. 1) in the two halves 14A, 14B of the housing 14. This pinching of the dispensing tube 12 substantially completely obstructs the dispensing tube 12, inhibiting material flow past the closure member 34. Typically, the half 14B opposite the half 14A having the plunger aperture 22 includes a strike plate (not shown) for the plunger, typically formed from aluminum, that is integrated into the back wall 36 of the passageway to be in registration with the plunger aperture 22.
When it is desired to dispense material, the solenoid (not shown) is actuated to move the solenoid plunger 16 into the “active” or “open” position, as shown in FIG. 2B, for a fixed period of time before disengaging the solenoid and allowing the solenoid plunger 16 to return to the “rest” or “closed” position shown in FIG. 2A. During the period of time that the solenoid plunger 16 is in the “active” or “open” position (FIG. 2B), the dispensing tube 12 is unobstructed and a predetermined volume of liquid or granular material is able to move past the position of the solenoid plunger 16 before the dispensing tube 12 is again obstructed as the solenoid plunger 16 returns to the “rest” or “closed” position (FIG. 2A).
The plunger head 26 is secured to the armature shaft 24 by way of a tab 38 extending from the base 28 of the plunger head 26 and which is received in a corresponding slot 40 at the end of the armature shaft 24 and held in place by a rivet 42.
When a reservoir of the material being metered, such as a bag of cream or milk, is empty and must be replaced, a user will unscrew the thumbscrew 19 and then separate the two opposed halves 14A, 14B by pivoting the half 14B having the thumbscrew 19 away from the other half 14A, which is mounted to the dispenser, so as to expose the dispensing tube 12. This enables the user to remove the empty bag and its associated dispensing tube 12 and install a new, full bag and insert the associated new dispensing tube 12 into the channel 20A. The user then pivots the half 14B having the thumbscrew 19 back toward the other half 14A, trapping the new dispensing tube 12 in the vertical passageway 20, and then screws the thumbscrew 19 back into the threaded aperture 21. This procedure is time consuming, especially in the context of a quick-service restaurant, where seconds count and customers expect to be served in less than a minute. Moreover, with repeated use, the thumbscrew 19 may develop a tendency to bind in the threaded aperture 21, making it more difficult to screw and unscrew and thereby increasing both the difficulty of changing the reservoir as well as the time required to do so.
In addition, the barrel portions 18B of the plastic hinge 18 joining the two halves 14A, 14B are prone to breakage, as shown by the arrow “B” in FIG. 2. Such breakage requires that the entire housing 14 be replaced, necessitating a costly maintenance call and also requiring that the metering dispenser be taken out of service.